The various peripherals for handling semiconductor workpiece lots are exemplified herein for the purposes of example by wafer cassettes, generally referred to herein as “cassettes” unless otherwise specified for particular instances. Practitioners of the relevant arts will recognize the broader applicability of the background, description, claims, drawings, and requisite skill in the arts to semiconductor manufacturing peripherals in general.
In the manufacturing of electronic semiconductor devices, it is common to fabricate numerous chips on a semiconductor wafer. It is also common to process chips in manufacturing lots contained by a tray, magazine, or other conveyance, or “peripheral” for holding multiple workpieces. During the manufacturing process, it is often desirable to handle the workpieces, wafers for example, for conveyance to equipment used for various processes involved in manufacturing, such as implantation, photo-resist, cleaning, and testing. In general, wafers are handled in production lots, commonly twenty-five wafers, held in a horizontal orientation in an apparatus such as a cassette, magazine, tray, rack, or carrier. The cassettes perform the function of segregating and safely holding and conveying the wafers during movement from one piece of equipment to another for processing. Several variations of wafer cassettes may be used, depending on the particular manufacturing process being performed. For example, Teflon (a registered trademark of E. I. du Pont de Nemours and Company) cassettes may be employed to hold the wafers while they are in chemical processes, ABS (acrylonitrile butadiene styrene) or other plastic traveler cassettes may be used to transport wafers from one process area to the next, and quartz or stainless steel cassettes may be employed to retain wafers during high temperature processes.
Semiconductor chip manufacturing equipment typically includes processing equipment serviced by robotic apparatus such as a transfer blade used for transferring wafers one-at-a-time to the processing equipment from a wafer cassette. Typically, the cassette is loaded into a cassette support position provided on or adjacent to the equipment. In general, a wafer cassette has multiple slots for accommodating the individual wafers, and the wafer cassette itself is loaded onto a wafer cassette support. While the cassette is stationary in the support, each wafer is taken out of its respective slot of the wafer cassette and is transferred to the processing or testing equipment by a robotic transfer blade. Similarly, processed wafers are removed from the processing equipment and replaced in their respective slots by the robotic transfer blade. Inherent in such processes and systems is the requirement for precise mechanical alignment of the transfer blade with the wafers. It is known in the arts to visually or mechanically align the top and/or bottom of the cassette with the transfer blade mechanism. In systems known in the arts, it is generally assumed that alignment of the top and/or bottom of the cassette relative to the equipment equates to alignment of the wafers held by the cassette with the transfer blade. This approach can lead to unfavorable surprises in situations when the assumption of alignment is incorrect. For example, if a particular cassette is outside of the dimensions required for the particular application, which may occur due to causes such as defects, damage, or wear, misalignment may occur, possibly leading to process delays, damage to wafers, or contamination of nearby wafers and equipment due to debris from wafer breakage.
These and other problems in making precise wafer cassette alignment lead to additional difficulties such as increased time required to perform the manufacturing processes, decreased yield due to improper alignment, and damaged wafers and equipment. Problems similar to those discussed in the illustrative example including wafer cassettes exist for other peripherals for handling wafers or other workpieces such as manufacturing lots of individual chips. It would be desirable in the arts to develop apparatus, systems, and methods providing improved dimensional verification of peripherals to ensure proper alignment relative to other manufacturing and testing equipment. Such improvements would provide advantages, such as reduced cycle time, increased yield, improved accuracy, and convenience. The present invention is directed to overcoming, or at least reducing the effects of one or more of the problems present in the arts.